The suspension of vehicles by means of rotary support arms of suspension of each of the wheels is well known in the prior art and has given rise to numerous applications in the field of automobile vehicle suspension where the rotary arm is advantageously rendered integral in rotation with one of the ends of a torsion arm the other end of which is secured to the vehicle chassis. These compact and practical dispositions are unfortunately not applicable to motorcycle which are not sufficiently wide to transversally house a torsion arm spring.
In the field of motor-cycles, is generally utilized as suspension spring a helical spring incorporated around a hydraulic shock-absorbing jack, the shock-absorbing qualities of which can be rapidly adjusted through the intermediary of cogs or screws. In order to allow the adjustment of these spring-shock-absorbing devices, it is necessary to have good manual accessibility to said device, so as to be able to act upon it with adjusting and screwing tools. It has already been proposed to do this through hinging one end of the shock-absorber underneath the motorcycle engine between the engine and the rolling path in order to prevent the shock-absorber from being inserted into suspension rods and arms.
Successive amplication push-rod systems are, furthermore, utilized with this shock-absorbing disposition underneath the engine in order to obtain stretching of the shock-absorber on the rebounce, i.e. expansion of the suspension and to provide that, for an equivalent angle of rotation of the support arm, the stroke of the actuating rod of the shock-absorber spring is variable as a function of the compression of the suspension in order to cause to vary the stiffness of the suspension and/or of the shock-absorber in function of the compression of the suspension. This stiffness generally increases with the compression of the suspension until the suspension is abutting on elastomeric stroke-end stops which thus increases the stiffness of the suspension in a very sudden manner without completely suppressing the resilience of the suspension.
One of the aims of the present invention is specifically to overcome the defects and shortcomings observed in service on rotary arm suspension devices utilizing a spring-shock-absorber assembly intended to be housed in an area offering good adjustment accessibility underneath the engine. The invention aims at allowing the introduction of the spring-shock-absorbing device in a free zone located underneath the engine while connecting it to the support arm by hinges located on the side of the engine block and thus less exposed to projections from the road than the lower part of the engine.